Valleyview
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Valleyview clear sky chart from 2005-11-05 to 2017-09-24.

This page is a summary of past forecasts. Even though it's based only on forecasts, some people use these pages as clue to a site's climate. But climate data based on actual observation should be preferred (if you can find it!).

Cloud, Transparency and Seeing forecasts are summarized individually. But because good observing conditions require a combination of minimum cloud cover, transparency and seeing, the individual forecast summaries can be difficult to interpret. The observing conditions section counts the combinations of conditions needed for common types of astronomical observation.

Observing Conditions

The following tables count the occurrence of the combinations of forecast and darkness conditions needed for different observations. Conditions are rated by by what percentage of the hours the observation would likely be attempted are usable.
Observation TypeMinimum conditions for hour to be usableOut of hours
Clear of CloudsTransparencySeeingSky Brightness
Planetary:50%(no limit)Average(no limit)Nighttime Hours
Deep Sky:70%Average(no limit)5.9Nighttime Hours
CCD Imaging:70%Below AveragePoor(no limit)Nighttime Hours

Percentages are of nighttime hours per month, or per year, when a particular observing conditions was met. Deep Sky percentages never exceed 50% because the moon is up half the time. Deep sky percentages are much lower for charts at high latitudes because of fewer dark hours in the summer.

Overall

PlanetaryData
Pts
Deep Sky
Max 60%
Data
Pts
Both Planetary and Deep Sky
Max 60%
Data
Pts
Either Planetary or Deep SkyData
Pts
CCD ImagingData
Pts
Night
38%
15119
9%
46748
6%
15094
42%
15094
17%
34191

By Month

MonthDays of MonthPlanetaryData
Pts
Deep Sky
Max 60%
Data
Pts
Both Planetary and Deep Sky
Max 60%
Data
Pts
Either Planetary or Deep SkyData
Pts
CCD ImagingData
Pts
January1st to 15thNight
33%
925
7%
2865
5%
925
35%
925
12%
2254
January16th to endNight
27%
868
12%
2861
9%
868
32%
868
13%
2147
February1st to 15thNight
36%
700
9%
2464
7%
700
39%
700
14%
1813
February16th to endNight
44%
632
11%
2025
10%
632
48%
632
17%
1468
March1st to 15thNight
32%
720
12%
2160
7%
720
38%
720
16%
1625
March16th to endNight
40%
768
13%
2019
7%
767
42%
767
19%
1529
April1st to 15thNight
34%
662
11%
1742
6%
662
37%
662
18%
1330
April16th to endNight
38%
429
9%
1509
8%
429
42%
429
14%
1104
May1st to 15thNight
45%
359
4%
1341
3%
359
46%
359
17%
911
May16th to endNight
45%
374
0%
1222
0%
374
45%
374
19%
853
June1st to 15thNight
46%
360
0%
1080
0%
360
46%
360
17%
798
June16th to endNight
55%
360
0%
1080
0%
360
55%
360
20%
756
July1st to 15thNight
60%
340
0%
1020
0%
340
60%
340
21%
708
July16th to endNight
56%
376
0%
1138
0%
354
57%
354
21%
764
August1st to 15thNight
64%
360
4%
1432
6%
358
65%
358
22%
846
August16th to endNight
50%
478
12%
1624
12%
478
54%
478
20%
1078
September1st to 15thNight
54%
713
13%
1793
8%
713
56%
713
31%
1190
September16th to endNight
43%
692
16%
1902
8%
692
48%
692
25%
1309
October1st to 15thNight
39%
660
14%
2011
9%
660
45%
660
18%
1439
October16th to endNight
32%
704
11%
2288
6%
704
39%
704
15%
1673
November1st to 15thNight
28%
823
12%
2556
9%
823
33%
823
14%
1918
November16th to endNight
27%
900
9%
2700
4%
900
31%
900
12%
2129
December1st to 15thNight
29%
924
10%
2844
6%
924
32%
924
12%
2246
December16th to endNight
33%
992
11%
3072
6%
992
38%
992
15%
2303

Individual Forecasts

The length of each colored bar in the "occurrence of each Forecast" column is proportional to the number of times the chart forecast that color. The percentages are of the total number of hours per month, or per year, with a particular forecast. The colors as the same as those used in clear sky charts.

Note: Transparency probabilities are only counted for those hours that have 30% or less cloud cover. Seeing probabilities are only counted for those hours that have 80% or less cloud cover. If that's too tricky, try Observing Conditions instead.

Overall

Occurrence of each ForecastData
Points
Cloud CoverDay
11%9%47%6%36%5%6%7%30%
48238
Night
9%11%5%8%7%45%5%6%7%29%
46879
TransparencyDay
50%8%16%18%5%
47873
Night
52%7%14%18%6%
46749
SeeingDay
16%6%24%28%18%4
6841
Night
16%6%26%32%15%2
15130

By Month

Percentage Cloud Cover NW (2006-)
Color Meanings:
Overcast 90% covered 80% covered 70% covered 60% covered 50% covered 40% covered 30% covered 20% covered 10% covered Clear
MonthDays in MonthOccurrence of each ForecastData
Points
January1st to 15thDay
8%14%6%10%7%36%6%5%6%22%
1074
16th to endDay
10%13%5%9%5%47%5%5%6%26%
1372
February1st to 15thDay
9%9%5%8%7%5%5%5%6%7%27%
1400
16th to endDay
6%12%9%10%8%47%7%47%22%
1447
March1st to 15thDay
6%13%7%8%8%45%5%5%6%26%
1800
16th to endDay
7%13%5%10%5%36%6%6%8%25%
2202
April1st to 15thDay
7%12%5%8%7%36%5%7%7%28%
2206
16th to endDay
12%10%48%8%47%6%5%7%25%
2451
May1st to 15thDay
11%6%36%8%46%5%7%8%32%
2610
16th to endDay
14%9%46%6%36%5%6%7%29%
2888
June1st to 15thDay
17%7%37%6%36%5%6%8%26%
2880
16th to endDay
13%6%37%5%45%5%6%9%33%
2880
July1st to 15thDay
14%5%25%6%25%5%6%8%37%
2880
16th to endDay
10%5%25%5%36%6%8%10%36%
2949
August1st to 15thDay
8%6%36%5%36%5%6%9%38%
2520
16th to endDay
12%6%26%6%46%6%6%9%33%
2578
September1st to 15thDay
12%7%36%5%3445%6%39%
2166
16th to endDay
13%7%35%5%35%438%39%
1916
October1st to 15thDay
13%10%37%6%45%46%7%30%
1618
16th to endDay
10%13%47%5%345%5%8%29%
1584
November1st to 15thDay
10%14%5%8%6%35%5%6%5%27%
1289
16th to endDay
6%12%5%11%8%45%5%47%27%
1260
December1st to 15thDay
10%16%7%10%8%35%5%2424%
1116
16th to endDay
6%11%6%11%8%35%6%5%7%26%
1152
January1st to 15thNight
7%14%6%10%8%5%6%5%46%23%
2865
16th to endNight
8%14%5%8%7%45%46%7%26%
2861
February1st to 15thNight
9%11%5%9%8%45%447%27%
2452
16th to endNight
411%6%10%7%47%6%6%7%27%
2025
March1st to 15thNight
8%14%410%7%45%46%7%26%
2160
16th to endNight
8%13%5%9%6%36%46%9%26%
2016
April1st to 15thNight
8%10%5%11%8%35%5%6%6%27%
1742
16th to endNight
13%10%5%8%7%45%45%8%26%
1509
May1st to 15thNight
9%7%5%7%7%46%5%6%8%30%
1340
16th to endNight
16%9%35%5%27%5%6%7%30%
1222
June1st to 15thNight
13%9%28%7%46%46%8%28%
1080
16th to endNight
14%6%25%5%46%5%6%8%32%
1080
July1st to 15thNight
9%435%6%46%7%8%8%35%
1080
16th to endNight
11%6%25%447%6%6%10%34%
1217
August1st to 15thNight
7%425%6%25%5%7%8%43%
1440
16th to endNight
10%5%25%7%37%5%6%9%36%
1624
September1st to 15thNight
9%7%36%42445%9%43%
1793
16th to endNight
12%5%35%4445%6%9%37%
1902
October1st to 15thNight
12%9%38%6%35%5%6%7%32%
2011
16th to endNight
11%11%47%5%45%5%6%8%28%
2288
November1st to 15thNight
11%15%6%8%6%35%45%6%27%
2556
16th to endNight
7%16%7%10%8%44445%25%
2700
December1st to 15thNight
8%15%5%10%8%45%5%5%7%22%
2844
16th to endNight
5%13%7%9%7%5%6%5%6%7%25%
3072

Transparency (when cloud cover <= 30%)
Color Meanings:
Too cloudy to forecast Poor Below Average Average Above average Transparent
MonthDays in MonthOccurrence of each ForecastData
Points
January1st to 15thDay
61%6%14%11%41
1074
16th to endDay
58%6%12%12%7%1
1372
February1st to 15thDay
54%9%15%13%6%
1400
16th to endDay
60%7%14%12%4
1447
March1st to 15thDay
55%7%15%16%4
1800
16th to endDay
53%9%17%16%2
2202
April1st to 15thDay
51%8%13%18%7%
2206
16th to endDay
54%8%12%16%7%
2451
May1st to 15thDay
46%7%14%19%11%
2610
16th to endDay
50%7%12%18%10%
2893
June1st to 15thDay
53%8%14%18%4
2880
16th to endDay
46%8%16%21%7%
2880
July1st to 15thDay
43%7%16%24%6%
2711
16th to endDay
41%11%22%20%4
2765
August1st to 15thDay
40%10%24%21%3
2503
16th to endDay
45%9%20%19%4
2578
September1st to 15thDay
44%7%19%22%5%
2166
16th to endDay
44%8%15%23%7%
1916
October1st to 15thDay
50%9%16%20%2
1618
16th to endDay
52%9%16%18%2
1584
November1st to 15thDay
55%6%15%16%5%
1289
16th to endDay
56%7%15%15%41
1260
December1st to 15thDay
64%7%11%13%3
1116
16th to endDay
56%7%15%13%7%
1152
January1st to 15thNight
61%6%14%13%31
2865
16th to endNight
56%6%13%14%6%1
2861
February1st to 15thNight
55%6%15%15%6%
2464
16th to endNight
52%7%17%16%5%
2025
March1st to 15thNight
56%6%13%18%6%
2160
16th to endNight
53%6%12%19%8%
2020
April1st to 15thNight
55%6%10%17%8%1
1742
16th to endNight
54%8%10%17%8%
1509
May1st to 15thNight
48%7%8%21%12%
1341
16th to endNight
49%6%11%19%12%
1222
June1st to 15thNight
52%8%12%21%4
1080
16th to endNight
47%7%16%21%6%
1080
July1st to 15thNight
41%13%14%22%8%
1020
16th to endNight
41%10%21%21%4
1138
August1st to 15thNight
35%10%22%25%5%
1432
16th to endNight
42%9%20%21%6%
1624
September1st to 15thNight
38%6%19%26%7%1
1793
16th to endNight
41%9%16%23%9%
1902
October1st to 15thNight
49%7%14%23%4
2011
16th to endNight
53%7%16%19%2
2288
November1st to 15thNight
57%6%12%18%5%
2556
16th to endNight
60%7%12%13%31
2700
December1st to 15thNight
61%7%11%14%3
2844
16th to endNight
56%7%14%17%5%
3072

Seeing (when cloud cover <= 80%)
Color Meanings:
Too cloudy to forecast Bad 1/5 Poor 2/5 Average 3/5 Good 4/5 Excellent 5/5
MonthDays in MonthOccurrence of each ForecastData
Points
January1st to 15thDay
16%5%11%35%20%11%
60
16th to endDay
9%128%28%20%12%
64
February1st to 15thDay
13%8%28%40%8%1
60
16th to endDay
11%430%28%22%2
170
March1st to 15thDay
17%12%33%23%10%1
270
16th to endDay
17%432%29%13%2
288
April1st to 15thDay
16%13%28%28%11%2
269
16th to endDay
21%11%26%26%12%1
270
May1st to 15thDay
13%9%22%31%18%4
387
16th to endDay
20%420%30%19%4
603
June1st to 15thDay
19%6%21%25%23%4
675
16th to endDay
16%419%29%21%7%
675
July1st to 15thDay
15%421%29%24%4
645
16th to endDay
13%421%32%22%6%
617
August1st to 15thDay
11%5%19%28%25%9%
315
16th to endDay
14%9%30%28%15%
332
September1st to 15thDay
19%7%21%26%17%6%
315
16th to endDay
19%12%27%25%12%3
288
October1st to 15thDay
21%7%28%27%12%2
195
16th to endDay
21%118%36%17%4
96
November1st to 15thDay
15%11%44%22%41
63
16th to endDay
11%5%23%38%8%13%
60
December1st to 15thDay
15%325%23%23%10%
60
16th to endDay
10%10%23%25%17%12%
64
January1st to 15thNight
17%8%25%32%13%2
930
16th to endNight
18%10%30%29%10%
868
February1st to 15thNight
16%6%26%28%17%3
704
16th to endNight
11%323%37%20%3
632
March1st to 15thNight
14%6%31%32%11%2
720
16th to endNight
16%325%35%16%2
768
April1st to 15thNight
14%6%30%30%16%1
662
16th to endNight
20%6%22%33%16%1
429
May1st to 15thNight
13%5%22%37%17%2
360
16th to endNight
21%222%34%17%2
375
June1st to 15thNight
20%319%31%24%1
360
16th to endNight
19%117%36%22%3
360
July1st to 15thNight
10%315%39%28%2
340
16th to endNight
14%217%36%25%3
376
August1st to 15thNight
10%114%36%30%6%
360
16th to endNight
13%227%34%21%1
478
September1st to 15thNight
15%218%38%21%2
713
16th to endNight
15%6%28%31%15%2
692
October1st to 15thNight
19%5%25%35%12%
660
16th to endNight
21%7%28%31%10%1
704
November1st to 15thNight
21%8%33%27%8%1
823
16th to endNight
16%9%29%29%12%2
900
December1st to 15thNight
18%8%30%28%11%2
924
16th to endNight
13%7%28%31%15%3
992
Page generated at 2017-09-25 07:02:29. Version ac04

Copyright 2017 A. Danko


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